Method and apparatus for heating oil sands



Dec. 10, 1963 c. A. CARPENTER 3,113,622

METHOD AND APPARATUS FOR HEATING on. SANDS Filed Oct. 14. 1959 IN VEN TOR.

Arrows/5) 3,113,622 Patented me. 10, 1963' ice 3,113,622 METHOD AND APPARATUS FOR HEATING OIL SANDS Clayton A. Carpenter, Yerington, Nev., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Oct. 14, 1959, Ser. No. 846,354 8 Claims. (Cl. 166-39) This invention relates to a method'and apparatus for heating subterranean oil-bearing sands while producing oil therefrom, and more particularly concerns a method and apparatus for heating the upper zone of a relatively thick production interval without suppressing the production of oil from subjacent oil sands.

Oil-bearing sands, particularly in California, frequently occur as thin or shallow beds distributed over thick intervals. The exact spacing and thickness of the beds are, of course, widely varied; for instance, a production interval 1,000 feet thick may traverse many thin beds of oil sands which may only be 2 feet thick and may be spaced from 2 to 20 or more feet apart throughout its depth. Usually the well bore is drilled to the lowermost of such beds and the well is completed by perforating the casing throughout the length of the interval so that oil is produced simultaneously from all the beds traversed. Although this type of operation is satisfactory for normal primary production from the interval, it does not lend itself satisfactorily to the stimulation of production by the application of heat with conventional well heating methods and apparatus.

Oil wells are conventionally heated by maintaining a pool or column of production liquids in the annulus between the casing and production tubing and immersing a liquid heater in this pool to supply heat thereto. The heater is usually positioned in the lower region of the pool, to create convection currents which aid in the transmission of heat to the surrounding formation. The thickness of the zone which is heated can be readily controlled by raising or lowering the level of the pool; however, when the level of the pool is raised sufliciently to heat the upper region of a thick interval, the hydraulic head which it exerts suppresses oil production from the oil sand beds located in the lower part in the interval. When this interval is very thick, e.g., 500 or more feet, the hydraulic head is generally great enough to stop oil production completely from the lower sands.

It is a purpose of this invention to provide a method and apparatus for heating the upper regions of a thick production interval while permitting simultaneous oil production from all the oil sand beds within the production interval.

This purpose is achieved in accordance with the invention by maintaining a well bore a heated column of production liquid adjacent the upper portion of the production interval and transferring liquid from said column to the lower portion of the well bore while maintaining a relatively low pressure therein, and pumping liquid from said lower portion of the well bore to the earths surface through production tubing string extending through said column of liquid. The liquid column can be supported within the well bore adjacent the upper portion of the production interval by a packer positioned between the production tubing and the well casing or the walls of the bore. The height of the column is controlled by positioning a back pressure control in the packer set to maintain a back pressure equal to the hydraulic head of liquid corresponding to the thickness of the zone to be heated. Alternatively, the height of the liquid column can be controlled, without use of a back pressure control valve by extending an open ended conduit upwardly through the packer to the upper level of the zone to be heated. This conduit functions as an overflow, and fluids rising above its upper open end enter therein and flow by gravity to the zone beneath the packer.

A heater, preferably an electric well heater, is immersed within the liquid column, to supply heat thereto. Preferably this heater is positioned within the lower regions of the liquid column, particularly when the overflow conduit is chosen as the means to maintain the liquid level, since convection currents are thereby established within the column which aid in heat transfer to the surrounding formation. It is within the scope of the invention, however, to locate the heater elsewhere within the liquid column, particularly when the back pressure valve is the means employed to maintain the liquid column level.

The invention will be more completely described by reference to the drawings, of which:

FIGURE 1 illustrates the invention with the overflow conduit, and

FIGURE 2 illustrates the invention with the back pressure control valve.

Referring now to FIGURE 1, a well bore, lined with a perforated casing 2 and containing a central production tubing 1, is shown to traverse a thick production interval containing a plurality of oil sand beds such as A, B, C K and L, which are separated by non-producing strata. A packer 5 is positioned at the base of the upper region of the production interval which is to be heated, and an overflow conduit 6 concentrically positioned around the production tubing extends from its lower end below packer 5 through packer 5 to its upper end at the upper level of the zone to be heated. Oonduit 6 is sufficiently large in diameter to provide an annulus surrounding the production tubing. An electric heater 8 is positioned around the lower portion of the conduit directly above packer 5, and is connected to a suitable current source at the surface by an electrical conductor, not. shown. Beneath packer 5, the production tubing extends to the base of the bore hole and can be provided with a pump, when necessary, to remove production liquid from the well. Production liquid which enters the borehole through the casing above packer 5 is heated and flows by convection to the top of column 3 where it spills into the annulus between conduit 6 and production tubingfl-l to drain into the borehole beneath the packer where it mixes in pool 7 with production liquid from subjacent oil sands traversed by the lower region of the borehole. Pool 7 is maintained at any desired level by withdrawal of production liquid through production tubing 1. Thus it is apparent that the method and apparatus of the invention enable heating of selected oil sand beds Within a production interval without imposing a hydraulic head on subjacent oil sand beds.

Referring now to FIGURE 2, an alternative embodiment is shown 'within a borehole traversing a similar production interval, lined with a perforated casing 9, and containing a central production tubing '15. Between the production tubing and the casing, at the base of the zone to be heated, is positioned a packer -11 which contains a liquid passageway closed by a back pressure valve 12 set to maintain a constant back pressure equal to the hydraulic head exerted by the column of production liquid 13 which extends upwardly adjacent that portion of the interval which is to be heated. An electric heater 10 suitably connected to a current source is immersed at any desired level with-in this column of liquid. Production liquid enters the column of liquid through the perforated casing, is heated by heater 10, and passes through valve 12 into the space below the packer where it mixes with the production liquid entering from the subjacent oil sand beds in pool 14. Production liquid is withdrawn from pool 14 through central production tubing 15.

It is of course apparent that modifications other than those illustrated can be made without departing from the inventive concept. For example, it is within the scope of the invention to apply this technique to well bores which are not lined with a casing when the surrounding sands are well consolidated. Other liquid heaters can be used, e.g., a heated fluid such as steam, hot oil, water can be pumped into the well bore and either directly discharged into the liquid column or passed through a finned tube heat exchanger immersed within the column and returned to above ground. A submerged combustion heater immersed within the column of liquid can also be employed. When the distribution of the oil sand beds is known with sufficient accuracy, it is within the scope of the invention to position the column of heated production liquid adjacent those sand beds which respond most readily to heating. It is also within the scope of the invention to employ a plurality of columns of liquid at selected levels throughout the production interval by installing more than one packer with its associated back pressure relief valve or open ended overflow conduit.

It is thus apparent that the invention as it has been describe-d is applicable to the heating of subterranean oilbearing sands and is particularly suited for the heating of upper oil-bearing sand beds or regions thereof while permitting the simultaneous production of oil from subjacent oil sand beds or regions thereof.

Having completely, clearly and concisely described my invention, I therefore claim:

1. The method of heating a zone of oil-bearing sands constituting the upper portion of a subterranean production interval traversed by a well bore while simultaneously producing oil from said interval which comprises: packing off said well bore at the base of said zone and positioning upon the packing means a column of production liquid within said well bore opposite said zone with the base of said column adjacent the lower extremity of said zone, transferring heat to said column of liquid from a source of heat located therein, maintaining the upper level of said column substantially fixed at the upper extremity of said zone by transferring liquid from said column to a subjacent zone within said well bore and below said packing means thereby maintaining said subjacent zone at a pressure less than that exerted by a column of production liquid having a height equal to the vertical distance from said subjacent zone to the upper level of said liquid column, and withdrawing production liquid from said subjacent zone.

2. A method as defined in claim 1 wherein liquid is transferred from the top of said column to said subjacent zone.

3. A method as defined by claim 1 wherein said source of heat is an electric well heater supported in a production tubing string extending within the well bore.

4. An apparatus for heating a zone within a well bore having a centrally disposed production tubing for withdrawal of production fluids, said apparatus comprising a packer between said well bore and said centrally disposed production tubing, said packer being disposed at the base of said zone to be heated and having a passageway provided with pressure relief means set to maintain a pressure equal to the hydraulic head of a column of production liquid extending the height of said zone to be heated, heating means disposed immediately above said packer, said passageway communicating with a s-u'bjacent withdrawal zone and said production tubing extending into said withdrawal zone to permit removal of production fluids therefrom.

5. The apparatus of claim 4 wherein said heating means is an electric heater.

6. An apparatus for heating an upper zone of a production interval penetrated by a well bore comprising means for isolating the portion of said well bore traversing said upper zone from the subjacent portion of the well bore, a production tubing extending from the earths surface to said sulbjacent portion of said well bore, an open-ended conduit extending through said upper level of said subjacent portion of said well bore to the top of said upper zone and heating means surrounding said open ended conduit and positioned adjacent the lower end of said upper zone.

7. The apparatus of claim 6 wherein said production tubing extends concentrically through said conduit and the latter is of substantially greater diameter than said production tubing so as to form an annulus between said tubing and said conduit.

8. The apparatus of claim 6 wherein said heating means is an electric heater.

References Cited in the file of this patent UNITED STATES PATENTS 436,216 Copeland Sept. 9, 1890 1,634,085 Ryan June 28, 1927 2,703,621 Ford Mar. 8, 1955 OTHER REFERENCES Reistle, C. E., In: Paratiin and Congealing-Oil Problems, US. Bureau Mines, Bulletin 348, 1932, pages 92-97 relied on, 

1. THE METHOD OF HEATING A ZONE OF OIL-BEARING SANDS CONSTITUTING THE UPPER PORTION OF A SUBTERRANEAN PRODUCTION INTERVAL TRAVERSED BY A WELL BORE WHILE SIMULTANEOUSLY PRODUCING OIL FROM SAID INTERVAL WHICH COMPRISES: PACKING OFF SAID WELL BORE AT THE BASE OF SAID ZONE AND POSITIONING UPON THE PACKING MEANS A COLUMN OF PRODUCTION LIQUID WITHIN SAID WELL BORE OPPOSITE SAID ZONE WITH THE BASE OF SAID COLUMN ADJACENT THE LOWER EXTREMITY OF SAID ZONE, TRANSFERRING HEAT TO SAID COLUMN OF LIQUID FROM A SOURCE OF HEAT LOCATED THEREIN, MAINTAINING THE UPPER LEVEL OF SAID COLUMN SUBSTANTIALLY FIXED AT THE UPPER EXTREMITY OF SAID ZONE BY TRANSFERRING LIQUID FROM SAID COLUMN TO A SUBJACENT ZONE WITHIN SAID WELL BORE AND BELOW SAID PACKING MEANS THEREBY MAINTAINING SAID SUBJACENT ZONE AT A PRESSURE LESS THAN THAT EXERTED BY A COLUMN OF PRODUCTION LIQUID HAVING A HEIGHT EQUAL TO THE VERTICAL DISTANCE FROM SAID SUBJACENT ZONE TO THE UPPER LEVEL OF SAID LIQUID COLUMN, AND WITHDRAWING PRODUCTION LIQUID FROM SAID SUBJACENT ZONE. 